Opportunities for treating chronic hepatitis B and C virus infection using RNA interference

Evaluation of Interfering RNA Efficacy in Treating Hepatitis B: Is It Promising?

BACKGROUND

Despite an existing safe and effective vaccine for hepatitis B virus (HBV), it is still a major public health concern. Nowadays, several drugs are used to treat chronic hepatitis B; however, full healing remains controversial. The viral covalently closed circular DNA (cccDNA) formed by HBV forms a major challenge in its treatment, as does the ability of HBV to integrate itself into the host genome, which enables infection reactivation. Interfering RNA (RNAi) is a gene-silencing post-transcriptional mechanism which forms as a promising alternative to treat chronic hepatitis B. The aim of the present review is to assess the evolution of hepatitis B treatment approaches based on using RNA interference.

METHODS

Data published between 2016 and 2023 in scientific databases (PubMed, PMC, LILACS, and Bireme) were assessed.

RESULTS

In total, 76,949 articles were initially identified and quality-checked, and 226 eligible reports were analyzed in depth. The main genomic targets, delivery systems, and major HBV therapy innovations are discussed in this review. This review reinforces the therapeutic potential of RNAi and identifies the need for conducting further studies to fill the remaining gaps between bench and clinical practice.

shRNA transgenic swine display resistance to infection with the foot-and-mouth disease virus

Foot-and-mouth disease virus (FMDV) is one of the most important animal pathogens in the world. FMDV naturally infects swine, cattle, and other cloven-hoofed animals. FMD is not adequately controlled by vaccination. An alternative strategy is to develop swine that are genetically resistant to infection. Here, we generated FMDV-specific shRNA transgenic cells targeting either nonstructural protein 2B or polymerase 3D of FMDV. The shRNA-positive transgenic cells displayed significantly lower viral production than that of the control cells after infection with FMDV (P < 0.05). Twenty-three transgenic cloned swine (TGCS) and nine non-transgenic cloned swine (Non-TGCS) were produced by somatic cell nuclear transfer (SCNT). In the FMDV challenge study, one TGCS was completely protected, no clinical signs, no viremia and no viral RNA in the tissues, no non-structural antibody response, another one TGCS swine recovered after showing clinical signs for two days, whereas all of the normal control swine (NS) and Non-TGCS developed typical clinical signs, viremia and viral RNA was determined in the tissues, the non-structural antibody was determined, and one Non-TGCS swine died. The viral RNA load in the blood and tissues of the TGCS was reduced in both challenge doses. These results indicated that the TGCS displayed resistance to the FMDV infection. Immune cells, including CD3⁺, CD4⁺, CD8⁺, CD21⁺, and CD172⁺ cells, and the production of IFN-γ were analyzed, there were no significant differences observed between the TGCS and NS or Non-TGCS, suggesting that the FMDV resistance may be mainly derived from the RNAi-based antiviral pathway. Our work provides a foundation for a breeding approach to preventing infectious disease in swine.

Role of ellagic acid for the prevention and treatment of liver diseases

Globally, one of the alarming problems is the prevalence and burden of liver diseases, which accounts for 2 million cases per year. Chronic liver aetiologies such as hepatitis infections, alcoholic or non-alcoholic liver disease, environmental agents, and drug-induced toxicity are invariably responsible for liver fibrosis progression to finally hepatocellular carcinoma. Current treatment options are unable to overwhelm and cure liver diseases. Emerging findings suggest researchers' interest in using evidence-based complementary medicine such as ellagic acid with extensive pharmacological properties. They include antioxidant, anti-inflammatory, anti-hyperlipidaemic, anti-viral, anti-angiogenic, and anticancer activity. The molecular functions elicited by ellagic acid include scavenging of free radicals, regulation of lipid metabolism, the prohibition of fibrogenesis response-mediating proteins, inhibits hepatic stellate cells and myofibroblasts, restrains hepatic viral replication, facilitates suppression of growth factors, regulates transcription factors, proinflammatory cytokines, augments the liver immune response, fosters apoptosis and inhibits cell proliferation in tumorigenic cells. This review will most notably focus on preclinical and clinical information based on currently available evidence to warrant ellagic acid's prospective role in preventing liver diseases.

Promising approaches of small interfering RNAs (siRNAs) mediated cancer gene therapy

RNA interference (RNAi) has extensive potential to revolutionize every aspect of clinical application in biomedical research. One of the promising tools is the Small interfering RNA (siRNA) molecules within a cellular component. Principally, siRNA mediated innovative advances are increasing rapidly in support of cancer diagnosis and therapeutic purposes. Conversely, it has some delivery challenges to the site of action within the cells of a target organ, due to the progress of nucleic acids engineering and advance material science research contributing to the exceptional organ-specific targeted therapy. This siRNA based therapeutic technique definitely favors a unique and effective prospect to cancer patients. Herein, the significant drive also takes to review and summarize the major organ specific targets of diverse siRNAs based gene silencing mechanism. This machinery promisingly served as the inhibitor components for cancer development in the human model. Furthermore, the focus is also given to current applications on siRNA based quantifiable therapy leading to the silencing of cancer related gene expression in a sequence dependent and selective manner for cancer treatment. That might be a potent tool against the traditional chemotherapy techniques. Therefore, the siRNA mediated cancer gene therapy definitely require sharp attention like future weapons in opposition to cancer by the method of non-invasive siRNA delivery and effective gene silencing approaches.

MicroRNAs Expressed during Viral Infection: Biomarker Potential and Therapeutic Considerations

MicroRNAs (miRNAs) are short sequences of noncoding single-stranded RNAs that exhibit inhibitory effects on complementary target mRNAs. Recently, it has been discovered that certain viruses express their own miRNAs, while other viruses activate the transcription of cellular miRNAs for their own benefit. This review summarizes the viral and/or cellular miRNAs that are transcribed during infection, with a focus on the biomarker and therapeutic potential of miRNAs (or their antagomirs). Several human viruses of clinical importance are discussed, namely, herpesviruses, polyomaviruses, hepatitis B virus, hepatitis C virus, human papillomavirus, and human immunodeficiency virus.

Portulaca oleracea L. as a Prospective Candidate Inhibitor of Hepatitis C Virus NS3 Serine Protease

Hepatitis C virus (HCV) infection is a worldwide health problem affecting about 300 million individuals. HCV causes chronic liver disease, liver cirrhosis, hepatocellular carcinoma, and death. Many side effects are associated with the current treatment options. Natural products that can be used as anti-HCV drugs are thus of considerable potential significance. NS3 serine protease (NS3-SP) is a target for the screening of antiviral activity against HCV. The present work explores plants with anti-HCV potential, isolating possible lead compounds. Ten plants, used for medicinal purposes against different infections in rural areas of Pakistan, were collected. The cellular toxicity effects of methanolic extracts of the plants on the viability of Huh-7 cells were studied through the Trypan blue dye exclusion method. Following this, the anti-HCV potential of phytoextracts was assessed by infecting liver cells with HCV-3a-infected serum inoculum. Only the methanolic extract of Portulaca oleracea L. (PO) exhibited more than 70% inhibition. Four fractions were obtained through bioassay-guided extraction of PO. Subsequent inhibition of all organic extract fractions against NS3 serine protease was checked to track the specific target in the virus. The results showed that the PO methanolic crude and ethyl acetate extract specifically abridged the HCV NS3 protease expression in a dose-dependent fashion. Hence, PO extract and its constituents either alone or with interferon could offer a future option to treat chronic HCV.

Technical standards for hepatitis B virus X protein (HBx) research

Chronic infection with hepatitis B virus (HBV) is a risk factor for developing hepatocellular carcinoma (HCC). The life cycle of HBV is complex and has been difficult to study because HBV does not infect cultured cells. The HBV regulatory X protein (HBx) controls the level of HBV replication and possesses an HCC cofactor role. Attempts to understand the mechanism(s) that underlie HBx effects on HBV replication and HBV-associated carcinogenesis have led to many reported HBx activities that are likely influenced by the assays used. This review summarizes experimental systems commonly used to study HBx functions, describes limitations of these experimental systems that should be considered, and suggests approaches for ensuring the biological relevance of HBx studies.

Inhibition of HBV replication in vivo using helper-dependent adenovirus vectors to deliver antiviral RNA interference expression cassettes

BACKGROUND

HBV is hyperendemic to southern Africa and parts of Asia, but licensed antivirals have little effect on limiting life-threatening complications of the infection. Although RNA interference (RNAi)-based gene silencing has shown therapeutic potential, difficulties with delivery of anti-HBV RNAi effectors remain an obstacle to their clinical use. To address concerns about the transient nature of transgene expression and toxicity resulting from immunostimulation by recombinant adenovirus vectors (Ads), utility of RNAi-activating anti-HBV helper-dependent (HD) Ads were assessed in this study.

METHODS

Following intravenous administration of 5×10(9) unmodified or pegylated HD Ad infectious particles to HBV transgenic mice, HBV viral loads and serum HBV surface antigen levels were monitored for 12 weeks. Immunostimulation of HD Ads was assessed by measuring inflammatory cytokines, hepatic function and immune response to the co-delivered LacZ reporter gene.

RESULTS

Unmodified and pegylated HD Ads transduced 80-90% of hepatocytes and expressed short hairpin RNAs (shRNAs) were processed to generate intended HBV-targeting guides. Markers of HBV replication were decreased by approximately 95% and silencing was sustained for 8 weeks. Unmodified HD Ads induced release of proinflammatory cytokines and there was evidence of an adaptive immune response to β-galactosidase. However the HD Ad-induced innate immune response was minimal in preparations that were enriched with infectious particles.

CONCLUSIONS

HD Ads have potential utility for delivery of therapeutic HBV-silencing sequences and alterations of these vectors to attenuate their immune responses may further improve their efficacy.

Inhibition of hepatitis B virus replication in cultured cells and in vivo using 2'-O-guanidinopropyl modified siRNAs

Silencing hepatitis B virus (HBV) gene expression with exogenous activators of the RNA interference (RNAi) pathway has shown promise as a new mode of treating infection with the virus. However, optimizing efficacy, specificity, pharmacokinetics and stability of RNAi activators remains a priority before clinical application of this promising therapeutic approach is realised. Chemical modification of synthetic short interfering RNAs (siRNAs) provides the means to address these goals. This study aimed to assess the benefits of incorporating nucleotides with 2'-O-guanidinopropyl (GP) modifications into siRNAs that target HBV. Single GP residues were incorporated at nucleotide positions from 2 to 21 of the antisense strand of a previously characterised effective antiHBV siRNA. When tested in cultured cells, siRNAs with GP moieties at selected positions improved silencing efficacy. Stability of chemically modified siRNAs in 80% serum was moderately improved and better silencing effects were observed without evidence for toxicity or induction of an interferon response. Moreover, partially complementary target sequences were less susceptible to silencing by siRNAs with GP residues located in the seed region. Hydrodynamic co-injection of siRNAs with a replication-competent HBV plasmid resulted in highly effective knock down of markers of viral replication in mice. Evidence for improved efficacy, reduced off target effects and good silencing in vivo indicate that GP-modifications of siRNAs may be used to enhance their therapeutic utility.

Design of Synthetic shRNAs for Targeting Hepatitis C: A New Approach to Antiviral Therapeutics

Small hairpin RNAs (shRNAs) are widely used as gene silencing tools and typically consist of a duplex stem of 19–29 bp, a loop, and often a dinucleotide overhang at the 3′ end. Like siRNAs, shRNAs show promise as potential therapeutic agents due to their high level of specificity and potency, although effective delivery to target tissues remains a challenge. Algorithms used to predict siRNA performance are frequently used to design shRNAs as well. However, the differences between these two kinds of RNAi mediators indicate that the factors affecting target gene silencing will not be the same for siRNAs and shRNAs. Stem and loop lengths, structures of the termini, the identity of nucleotides adjacent to and near the loop, and the position of the guide (antisense) strand all affect the efficacy of shRNAs. In addition, shRNAs with 19-bp or shorter stem lengths are processed and function differently than those with longer stems. In this review, we describe studies of targeting the hepatitis C virus that have provided guidelines for an optimal design for short (19 bp) shRNAs (sshRNAs) that are highly potent, stable in biological fluids, and have minimal immunostimulatory properties.

Gene therapy of liver diseases: a 2011 perspective

Liver diseases including inherited metabolic disorders, chronic viral hepatitis, liver cirrhosis and primary and metastatic liver cancer constitute a formidable health problem because of their high prevalence and the important limitations of current therapies. Gene therapy, a procedure based on the transfer of therapeutic genes to tissues, has been used since the 1990s as a new approach to treating a number of incurable conditions. After a period of lights and shades recent success in treating several devastating diseases like inherited immune deficiency disorders, beta-thalassemia, or inherited blindness appear to herald a new era where gene therapy can be listed among standard therapy options for a wide variety of human conditions. In this review, we provide information illustrating the potentiality of gene therapy in the management of liver diseases lacking other effective therapies.

Countering hepatitis B virus infection using RNAi: how far are we from the clinic?

Globally, persistent HBV infection is a significant cause of public health problems. Currently available HBV therapies have variable efficacy and there is a need to develop improved treatment to prevent cirrhosis and hepatocellular carcinoma. Although RNA interference (RNAi)-based approaches have shown promise, accomplishing safe and sustained silencing by RNAi activators, as well as their efficient delivery to hepatocytes have hampered clinical translation of this very promising technology. Expressed silencers may be produced in a sustained manner from stable DNA templates, which makes them suited to treatment of chronic HBV infection. DNA expression cassettes can be incorporated into both viral and non-viral vectors, but in vivo delivery of these cassettes with non-viral vectors is currently inefficient. Synthetic short interfering RNAs (siRNAs), which may be chemically modified to improve stability, specificity and efficacy, are more conveniently delivered to their cytoplasmic sites of action with synthetic non-viral vectors. However, the short duration of action of this class of RNAi activator is a drawback for treatment of chronic HBV infection. Despite the impressive progress that has been made in developing highly effective HBV gene silencers, challenges continue to face implementation of RNAi-based HBV therapy. This review will discuss the current status of the topic and consider the developments that are required to advance RNAi-based HBV therapy to clinical application.

Effects of HBV Genetic Variability on RNAi Strategies

RNAi strategies present promising antiviral strategies against HBV. RNAi strategies require base pairing between short RNAi effectors and targets in the HBV pregenome or other RNAs. Natural variation in HBV genotypes, quasispecies variation, or mutations selected by the RNAi strategy could potentially make these strategies less effective. However, current and proposed antiviral strategies against HBV are being, or could be, designed to avoid this. This would involve simultaneous targeting of multiple regions of the genome, or regions in which variation or mutation is not tolerated. RNAi strategies against single genotypes or against variable regions of the genome would need to have significant other advantages to be part of robust therapies.

MicroRNA-like antivirals

Employing engineered DNA templates to express antiviral microRNA (miRNA) sequences has considerable therapeutic potential. The durable silencing that may be achieved with these RNAi activators is valuable to counter chronic viral infections, such as those caused by HIV-1, hepatitis B, hepatitis C and dengue viruses. Early use of expressed antiviral miRNAs entailed generation of cassettes containing Pol III promoters (e.g. U6 and H1) that transcribe virus-targeting short hairpin RNA mimics of precursor miRNAs. Virus escape from single gene silencing elements prompted later development of combinatorial antiviral miRNA expression cassettes that form multitargeting siRNAs from transcribed long hairpin RNA and polycistronic primary miRNA sequences. Weaker Pol III and Pol II promoters have also been employed to control production of antiviral miRNA mimics, improve dose regulation and address concerns about toxicity caused by saturation of the endogenous miRNA pathway. Efficient delivery of expressed antiviral sequences remains challenging and utilizing viral vectors, which include recombinant adenoviruses, adeno-associated viruses and lentiviruses, has been favored. Investigations using recombinant lentiviruses to transduce CD34+ hematological precursor cells with expressed HIV-1 gene silencers are at advanced stages and show promise in preclinical and clinical trials. Although the use of expressed antiviral miRNA sequences to treat viral infections is encouraging, eventual therapeutic application will be dependent on rigorously proving their safety, efficient delivery to target tissues and uncomplicated large scale preparation of vector formulations. This article is part of a special issue entitled: MicroRNAs in viral gene regulation.

RNA Interference inhibits hepatitis B virus of different genotypes in vitro and in vivo

Background

Hepatitis B virus (HBV) infection increases the risk of liver disease and hepatocellular carcinoma. Small interfering RNA (siRNA) can be a potential new tool for HBV therapy. Given the high heterogeneity of HBV strains and the sensitivity towards sequences changes of siRNA, finding a potent siRNA inhibitor against the conservative site on the HBV genome is essential to ensure a therapeutic application.

Results

Forty short hairpin RNA (shRNA) expression plasmids were constructed to target conserved regions among nine HBV genotypes. HBV 1.3-fold genome plasmids carrying various genotypes were co-transfected with shRNA plasmids into either Huh7 cells or mice. The levels of various viral markers were examined to assess the anti-HBV efficacy of siRNA. Four (B245, B376, B1581 and B1789) were found with the ability to potently inhibit HBV RNA, DNA, surface antigen (HBsAg), e antigen (HBeAg) and core antigen (HBcAg) expression in HBV genotypes A, B, C, D and I (a newly identified genotype) in Huh7 cells and in mice. No unusual cytotoxicity or off-target effects were noted.

Conclusions

Such siRNA suggests an alternate way of inhibiting various HBV genotypes in vitro and in vivo, promising advances in the treatment of HBV.

Does RNA interference provide new hope for control of chronic hepatitis B infection?

Hepatitis B virus (HBV) infection is a global human health problem, with an estimated 350 million people having chronic hepatitis B (CHB) infection worldwide. The majority of infections acquired during adulthood are resolved without intervention; however, infections acquired at birth or during early childhood have a 90% chance of progressing to CHB, leading to a host of adverse effects on the liver, including cirrhosis and cancer. CHB is currently treated with a combination of cytokines and/or nucleoside/nucleotide analogues; however, adverse side effects to cytokine therapy and the selection of resistance mutations to nucleoside analogues often abrogate the efficacy of treatment. The recent discovery that small interfering RNA and microRNA are active in mammalian cells suggests it might be possible to supplement existing HBV therapies with small RNA-based therapeutic(s).

Rational design of immunostimulatory siRNAs

Short-interfering RNAs (siRNAs) have engendered much enthusiasm for their ability to silence the expression of specific genes. However, it is now well established that siRNAs, depending on their sequence, can be variably sensed by the innate immune system through recruitment of toll-like receptors 7 and 8 (TLR7/8). Here, we aimed to identify sequence-based modifications allowing for the design of bifunctional siRNAs with both proinflammatory and specific silencing activities, and with potentially increased therapeutic benefits. We found that the introduction of a micro-RNA (miRNA)-like nonpairing uridine-bulge in the passenger strand robustly increased immunostimulatory activity on human immune cells. This sequence modification had no effect on the silencing efficiency of the siRNA. Increased immunostimulation with the uridine-bulge design was specific to human cells, and conserved silencing efficiency required a Dicer-substrate scaffold. The increased cytokine production with the uridine-bulge design resulted in enhanced protection against Semliki Forest virus (SFV) infection, in viral assays. Thus, we characterize a design scaffold applicable to any given siRNA sequence, that results in increased innate immune activation without affecting gene silencing. Our data suggest that this sequence modification coupled with structural modification differentially recruits human TLR8 over TLR7, and could have potential application in antiviral therapies.

Inhibition of hepatitis B virus replication with linear DNA sequences expressing antiviral micro-RNA shuttles

RNA interference (RNAi) may be harnessed to inhibit viral gene expression and this approach is being developed to counter chronic infection with hepatitis B virus (HBV). Compared to synthetic RNAi activators, DNA expression cassettes that generate silencing sequences have advantages of sustained efficacy and ease of propagation in plasmid DNA (pDNA). However, the large size of pDNAs and inclusion of sequences conferring antibiotic resistance and immunostimulation limit delivery efficiency and safety. To develop use of alternative DNA templates that may be applied for therapeutic gene silencing, we assessed the usefulness of PCR-generated linear expression cassettes that produce anti-HBV micro-RNA (miR) shuttles. We found that silencing of HBV markers of replication was efficient (>75%) in cell culture and in vivo. miR shuttles were processed to form anti-HBV guide strands and there was no evidence of induction of the interferon response. Modification of terminal sequences to include flanking human adenoviral type-5 inverted terminal repeats was easily achieved and did not compromise silencing efficacy. These linear DNA sequences should have utility in the development of gene silencing applications where modifications of terminal elements with elimination of potentially harmful and non-essential sequences are required.

siRNA delivery systems for cancer treatment

With increasing knowledge on the molecular mechanisms of endogenous RNA interference, small interfering RNAs (siRNAs) have been emerging as innovative nucleic acid medicines for treatment of incurable diseases such as cancers. Although several siRNA candidates for the treatment of ocular and respiratory diseases are undergoing clinical trials, there are challenges inherent in the further development of siRNAs for anti-cancer therapeutics, because systemic administration will be required in most cases. In addition to nonspecific off-target and immune stimulation problems, appropriate delivery remains a major hurdle. The technologies developed for delivery of nucleic acid medicines such as plasmid DNA and antisense oligonucleotides have paved the way to rapid progress for in vivo delivery of siRNAs. Here, we review various in vivo delivery strategies including chemical modification, conjugation, lipid-based techniques, polymer-based nanosystems, and physical methods. Moreover, the current progress in siRNA delivery systems for gynecologic, liver, lung, and prostate cancers is discussed.

Elucidating the encapsulation of short interfering RNA in PEGylated cationic liposomes

Short interfering RNA (siRNA) holds great potential for the treatment of hard-to-cure diseases. One of the major challenges to translate siRNA into drugs is its efficient delivery to its site-of-action, namely the cytoplasm of the target cells. Cationic liposomes have been shown to do the trick, but their short circulation lifetime and potential aggregation in blood limit their applicability for intravenous administration. These hurdles might be overcome by attaching poly(ethylene glycol) (PEG) at the surface of the cationic liposomes through the use of PEGylated lipids. However, this paper reveals that the classical mixing of siRNA with preformed PEGylated cationic liposomes, as frequently done to load PEGylated liposomes with siRNA, prevents an efficient encapsulation of the siRNA in the liposomes. We show that only a minor fraction of the siRNA becomes encapsulated in the core of the PEGylated liposomes, whereas a major part of the siRNA becomes bound at the liposome's outer surface. In serum, the surface-bound siRNA is immediately released and becomes degraded by serum nucleases. By contrast, hydrating a lipid film (containing PEGylated and cationic lipids) directly with a concentrated solution of siRNA (so-called HYDRA protocol), instead of mixing the siRNA with preformed PEGylated liposomes, encapsulates almost 50% of the siRNA in the core of the PEGylated liposomes, which is the maximal encapsulation efficiency for this type of complexes. We show that the siRNA encapsulated in the core of the thus obtained "HYDRA siPLexes" remains fully encapsulated upon dispersing the PEGylated liposomes in human serum.

Inhibition of hepatitis B virus gene expression and replication by artificial microRNA targeted ASGPR1

AIM: To investigate the inhibitory effects on hepatitis B virus (HBV) replication and expression by transfecting artificial microRNA targeted ASGPR1 into HepG2.2.15 cells.

METHODS: Three amiRNA-HBV plasmids were constructed and transfected into HepG2.2.15 cells via LipofectamineTM 2000 reagent. The level of ASGPR1 mRNA was measured by semi-quantitative RT-PCR. The level of ASGPR1 protein was measured by western blot. HBV antigen secretion was detected in the cells with transient and stable transfection by time-resolved fluoroimmunoassays (TRFIA). HBV DNA replication was examined by fluorescence quantitative PCR.

RESULTS: Three amiRNA significantly reduced ASGPR1 mRNA and protein expression, and the greatest reduction was seen in amiRNA-ASGPR1-610 transfected group. Expressions of ASGPR1 mRNA and protein were down-regulated by 57.3% and 49.8% at 72 h(P < 0.01). At the virus level, three amiRNA-ASGPR1 plasmids obviously inhibited the secretion of HBsAg and HBeAg with the greatest reduction seen in amiRNA-ASGPR1-610 transfected group. Expression levels of HBsAg and HBeAg were down-regulated by 31.3% and 33.6% after 72 h (P < 0.01) and HBV DNA level was down-regulated by 29.7% at 72 h (P < 0.01).

CONCLUSION: In HepG2.2.15 cells, HBV replication and expression could be inhibited by artificial microRNA targeted ASGPR1. Artificial microRNA targeted ASGPR1 could be a promising therapeutic approach for chronic HBV infection.

Natural products as promising drug candidates for the treatment of hepatitis B and C

Hepatitis B virus (HBV) or hepatitis C virus (HCV) infections are a major threat worldwide. Combination therapy of interferon-alpha and ribavirin is currently the treatment of choice for HCV-infected patients. However, this regimen is only effective in approximately 50% of patients and provokes severe side-effects. Numerous natural alternatives for treating HCV have been suggested. Deoxynojirimycin and its derivatives are iminosugars which exert anti-HCV activity by inhibiting alpha-glucosidases. A non-immunosuppressive derivate of cyclosporine A, NIM811, exerts anti-HCV activity by binding to cyclophilin. Other natural products with promising anti-HCV activity are 2-arylbenzofuran derivatives, Mellein, and pseudoguaianolides. For HBV treatment, several drugs are available, specifically targeting the virus polymerase (lamivudine, entecavir, telbivudine, and adefovir dipivoxil). The efficacy of these drugs is hampered by the development of resistance due to point mutations in the HBV polymerase. Due to drug resistance and adverse side-effects, the search for novel drugs is mandatory. Wogonin, ellagic acid, artemisinin and artesunate, chrysophanol 8-O-beta-D-glucoside, saikosaponin C, and protostane triterpenes are active against HBV. Natural products need to be investigated in more detail to explore their potential as novel adjuncts to established HBV or HCV therapy.

Comparative study of anti-hepatitis B virus RNA interference by double-stranded adeno-associated virus serotypes 7, 8, and 9

Using a hepatitis B virus (HBV) transgenic mouse model, we previously showed that a single dose of double-stranded adeno-associated virus (dsAAV) vector serotype 8 carrying a small hairpin RNA (shRNA) effectively reduces HBV replication and gene expression, but the effect gradually decreases with time. In this report, we compared the anti-HBV RNA interference (RNAi) effect of dsAAV8 with those of dsAAV7 and dsAAV9, two other hepatotropic AAV vectors, and examined whether the sequential use of these heterologous AAV vectors could prolong the anti-HBV effect. Our results showed that shRNA delivered by each of the three dsAAV vectors profoundly reduced the serum HBV titer and liver HBV mRNA and DNA levels in the transgenic mice for up to 22 weeks, with dsAAV8 having the greatest inhibitory effect, followed by dsAAV9 and dsAAV7. The potency of dsAAV8 correlated with the presence of higher levels of vector DNA and anti-HBV shRNA in the liver. An in vivo cross-administration experiment showed that preexisting anti-AAV8 antibody completely blocked the anti-HBV RNAi effect of dsAAV8, but had no effect on the potency of dsAAV7 and dsAAV9. Moreover, we demonstrated that a longer anti-HBV effect could be achieved by the sequential use of dsAAV8 and dsAAV9. These results indicate that effective and persistent HBV suppression might be achieved by a combination of the power of RNAi silencing effect and multiple treatments with different AAV serotypes.Molecular Therapy (2009) 17 2, 352-359 doi:10.1038/mt.2008.245.

MicroRNAs as targets for antisense-based therapeutics

MicroRNAs (miRNAs) are a novel class of endogenous non-coding single-stranded RNAs, which regulate gene expression post-transcriptionally by base pairing with their target mRNAs. So far > 5000 miRNA entries have been registered and miRNAs have been implicated in most, if not all, central cellular processes and several diseases. As the mechanism of action for miRNA regulation of target mRNAs is mediated by Watson-Crick base pairing, antisense oligonucleotides targeting the miRNAs appear as an obvious choice to specifically inhibit miRNA function. Indeed, miRNAs can be antagonized in vivo by oligonucleotides composed of high-affinity nucleotide mimics. Lessons learned from traditional antisense strategies and small-interfering RNA approaches, that is from potent nucleotide mimics, design rules, pharmacokinetics, administration and safety issues, are likely to pave the way for future clinical trials of miRNA-antagonizing oligonucleotides.

Molecular cloning of a pair of human pepsinogen A genes which differ by a Glu----Lys mutation in the activation peptide

Hepatitis C virus (HCV) belonging to the family Flaviviridae has infected 3% of the population worldwide and 6% of the population in Pakistan. The only recommended standard treatment is pegylated INF-α plus ribavirin. Due to less compatibility of the standard treatment, thirteen medicinal plants were collected from different areas of Pakistan on the basis of undocumented antiviral reports against different viral infections. Medicinal plants were air dried, extracted and screened out against HCV by infecting HCV inoculums of 3a genotype in liver cells. RT-PCR results demonstrate that acetonic and methanolic extract of Acacia nilotica (AN) showed more than 50% reduction at non toxic concentration. From the above results, it can be concluded that by selecting different molecular targets, specific structure-activity relationship can be achieved by doing mechanistic analysis. So, additional studies are required for the isolation and recognition of antiviral compound in AN to establish its importance as antiviral drug against HCV. For further research, we will scrutinize the synergistic effect of active antiviral compound in combination with standard PEG INF-α and ribavirin which may be helpful in exploring further gateways for antiviral therapy against HCV.